Human respiratory syncytial viruses, subtypes A and B (RSV A&B) and human parainfluenza virus types 1,2 and 3 (PIV-1,2,3) infections are the most common causes of acute lower respiratory tract infection in infants and children in the developed world. In the United States alone, close to 5 million children per year will be infected with the parainfluenza viruses. PIV-3 is second only to RSV as the major causative agent of bronchiolitis and pneumonia in infants. It is estimated that in the United States, approximately 600,000 children under the age of 6 develop laryngo-tracheo-bronchitis (croup) each year as a result of infection with PIV-1 and 2 and that approximately 1,000 infants may die as a result of PIV-3 infection. Approximately 10 to 15% of hospitalizations with bronchiolitis and pneumonia can be attributed to infection with PIV-3 with greater than 1.4 million infants in the United States suffering a clinically significant PIV-3 infection each year (ref. 1 -Throughout this application, various references are referred to in parenthesis to more fully describe the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosures of these references are hereby incorporated by reference into the present disclosure). Of those infected with PIV-3, 1 to 2% will require hospitalization and some children will die. The peak age for PIV-3 infections occurs at 2 to 4 months of age while PIV-associated croup peaks between 9 to 24 months of age. Reinfections are very common with the parainfluenza viruses, occurring most frequently with PIV-3.
Currently, safe and effective vaccines capable of protecting infants and young children from these viral infections are not available. Therefore, development of an effective parainfluenza vaccine is a priority.
Studies on the development of live viral vaccines and glycoprotein subunit vaccines against parainfluenza virus infection are being pursued. Clinical trial results with a formalin-inactivated PIV types 1,2,3 vaccine demonstrated that this vaccine was not efficacious (refs. 2, 3, 4). Further development of chemically-inactivated vaccines was discontinued after clinical trials with a formalin-inactivated RSV vaccine demonstrated that not only was the vaccine not effective in preventing RSV infection but many of the vaccinees who later became infected with RSV suffered a more serious disease. Most of parainfluenza vaccine research has focussed on candidate PIV-3 vaccines (ref. 5) with significantly less work being reported for PIV-1 and PIV-2. Recent approaches to PIV-3 vaccines have included the use of the closely related bovine parainfluenza virus type 3 and the generation of attenuated viruses by cold-adaptation of the virus (refs. 6, 7, 8, 9).
Another approach to parainfluenza virus type 3 vaccine development is a subunit approach focusing on the surface glycoproteins hemagglutinin-neuraminidase (HN) and the fusion (F) protein (refs. 10, 11, 12). The HN antigen, a typical type II glycoprotein, exhibits both haemagglutination and neuraminidase activities and is responsible for the attachment of the virus to sialic acid containing host cell receptors. The type I F glycoprotein mediates fusion of the viral envelope with the cell membrane as well as cell to cell spread of the virus. It has recently been demonstrated that both the HN and F glycoproteins are required for membrane fusion. The F glycoprotein is synthesized as an inactive precursor (F) which is proteolytically cleaved into disulfide-linked F2 and F1 moieties. While the HN and F proteins of PIV-1, 2 and 3 are structurally similar, they are antigenically distinct. Neutralizing antibodies against the HN and F proteins of one of PIV type are not cross-protective. Thus, an effective PIV subunit vaccine must contain the HN and F glycoproteins from the three different types of parainfluenza viruses. Antibody to either glycoprotein is neutralizing in vitro. A direct correlation has been observed between the level of neutralizing antibody titres and resistance to PIV-3 infections in infants. Native subunit vaccines for parainfluenza virus type 3 have investigated the protectiveness of the two surface glycoproteins. Typically, the glycoproteins are extracted from virus using non-ionic detergents and further purified using lectin affinity or immunoaffinity chromatographic methods. However, neither of these techniques may be entirely suitable for large scale production of vaccines under all circumstances. In small animal protection models (hamsters and cotton rats), immunization with the glycoproteins was demonstrated to prevent infection with live PIV-3 (refs. 13, 14, 15, 16, 17). The HN and F glycoproteins of PIV-3 have also been produced using recombinant DNA technology. HN and F glycoproteins have been produced in insect cells using the baculovirus expression system and by use of vaccinia virus and adenovirus recombinants (refs. 18, 19, 20, 21, 22). In the baculovirus expression system, both full-length and truncated forms of the PIV-3 glycoproteins as well as a chimeric F-HN fusion protein have been expressed. The recombinant proteins have been demonstrated to be protective in small animal models (see WO 91/00104, U.S. application Ser. No. 07/773,949 filed Nov. 29, 1991, assigned to the assignee hereof).
Parainfluenza virus infection may lead to serious disease. It would be advantageous to provide purified PIV glycoproteins and methods for their purification from native virus for use as antigens in immunogenic preparations including vaccines, carriers for other antigens and immunogens and the generation of diagnostic reagents.